Plants seeds are very sensitive to the surrounding environment, especially when they are stored for a prolonged period of time. The presence of moisture and oxygen at high temperatures is e.g. very detrimental to their survival and storability, and the presence of pathogenic organisms in a seed batch may further jeopardize the seeds' storability.
When seeds have been pre-treated before packaging, for example by means of priming, they often become even more sensitive to environmental factors and their storability decreases further. In commercial seed business it would be very desirable if seeds can be stored for a prolonged period of time without losing their viability and their ability to germinate (preferably quickly and simultaneously) to give rise to healthy and vigorous plants.
If seeds can be stored for a longer period of time, they can e.g. be kept until the next growing season if they had not been sold in time for sowing during the current season. If such seeds only have a limited storability, they would necessarily have to be thrown away, because their quality would no longer meet the high commercial standards at the time of the next growing season. This could represent a significant economic loss for the company or for the intermediary or end-user who had bought the seeds but had not sold or sown them in time.
Traditionally, seeds are preferably stored in cool and dry environments which requires investment in cooling infrastructure.
In the research leading to this invention, it was surprisingly found that oxygen absorbers may be used to increase the storability and long-term viability of living objects, in particular of living plant seeds, thereby largely abolishing the effects of temperature on seed storability. It was also found that oxygen absorbers that do not change the relative humidity of the atmosphere surrounding the stored seeds give better results.
Oxygen absorbers have previously been used in several environments and for various purposes. When attempting to preserve and store inanimate objects such as wood or metal, or food products, the presence of oxygen is usually undesired, because it allows the survival of aerobic micro-organisms (such as bacteria and fungi), worms and insects which may damage, eat or otherwise spoil the stored objects, and it allows the corrosion of metal objects, especially if the storage container has a high humidity. In such cases oxygen absorbers have been used to increase the storability of inanimate objects, by depleting the air inside the container of oxygen and moisture. Examples are their use for safely storing electronic equipment (which needs to be protected against oxygen-dependent corrosion), for preserving, transporting and storing archaeological artifacts made of metal, wood or bone (which may rapidly decay upon exposure to oxygen), for conserving works of art such as paintings or sculptures, or in the food industry. A common denominator in these described uses of oxygen absorbers is that the objects to be preserved are lifeless, easily destructible and often valuable.
In these previously described uses it is never an issue to keep the objects alive and/or to prolong their survival and viability, because they are lifeless or dead. Indeed, it is highly surprising that one can better store living objects and enhance their longevity by storage in an environment that is depleted of oxygen, while oxygen is essential for the survival of most higher organisms, including plants.
Atmospheric air consists of about 21 percent of oxygen (O2), about 78 percent of nitrogen (N2), and for the remaining fraction of other gases. Whereas oxygen is essential for the survival of aerobic organisms, its presence may sometimes be undesired. For example, the chemical reaction of oxygen with abiotic or biotic factors may lead to the generation of highly reactive molecules (such as reactive oxygen species, free radicals) that may cause damage to biological structures and molecules. In order to avoid such damage oxygen is usually flushed out by means of nitrogen or carbon dioxide. It was never contemplated before to absorb the oxygen.
In addition to increasing the storability and long-term viability of plant seeds directly, the research leading to this invention revealed that the use of oxygen absorbers during seed storage may also contribute to this same purpose by killing pathogenic or opportunistic organisms that may feed on the seeds or otherwise spoil them for further commercial use, and also by scavenging volatile compounds that are produced by some plant seeds. Some of these volatile compounds have allelopathic effects on other seeds (of the same or another plant species) when these are stored in vicinity of each other. An example of an allelopathic effect is inhibition of germination, which is highly undesired in a commercial context. During storage in confined areas (closed containers, rooms, refrigerators) such volatile compounds may accumulate to concentrations that are not commonly found under natural conditions, and this may have very strong effects on the germination rate of stored seeds.
The inventor's experiments showed that, for optimal commercial storage of plant seeds, the use of oxygen absorbers inside a seed storage container (such as a bag, a box, a cylinder, or any other type of packaging container, regardless of the material it is made of) has a very positive effect on the storability and long-term viability of the seeds, which leads to direct commercial advantages for the seed producer and for his customers.
Plant seeds are sold commercially to plant growers with the purpose of being sown to give rise to a healthy, well-performing population of crops that will yield as much harvestable material as possible. The harvestable material may e.g. include leaves, fruits, seeds, roots, tubers, flowers and/or stems.
Commercial plant seeds are often pre-treated to increase their performance. A common treatment is e.g. seed priming, which enables the seeds in a seed lot to germinate faster and more homogenously, by overcoming seed dormancy and by physiologically preparing the seeds for germination. A plant grower greatly benefits from a population of plantlets that germinate simultaneously, and that will proceed through their life cycle in a concerted manner. Also, plant seeds are often pilled and/or coated, which enables the addition of specific compounds to the seeds (such as germination-stimulating agents, or protective chemical agents that antagonize or discourage the growth of and colonization by undesired microorganisms or other organisms that could damage the seed and/or the germinating seedling). Furthermore, pilling and/or coating gives the seeds a uniform shape and size, which is advantageous when seeds are sown in a high-throughput manner, e.g. by means of an automated sowing machine.
A common disadvantage of priming and/or pilling methods, however, is that they often decrease the storability of seeds. When a seed-producing company produces commercial seed lots and proceeds to the stage of priming and/or pilling, it needs to sell the processed seeds within a certain time frame, in order for the seeds to still fulfill all required quality criteria at the time of sale, such as a very high germination rate and a very high percentage of usable transplants among the resulting plantlets. This time frame is highly dependent on the crop species, and often differences in storability are also observed between different varieties of a single crop. If the seeds cannot be sold in time they lose their commercial value, and this may represent a considerable economic loss for the seed-producing company. In the research leading to this invention it was observed that the use of oxygen absorbers significantly prolongs the storability of primed and/or pilled seeds.
The storage efficiency of living plant seeds is highly dependent on the storage environment, and it was observed that especially the surrounding temperature plays an important role herein. Seeds are often stored in a refrigerator (at about 4° C.) or in a freezer (at about −20° C.), because this generally improves the storability and the long-term viability maintenance of the seeds, but this approach requires an investment in cooling equipment, it incurs electricity costs, and it limits the available storage space to the space that can be cooled down to the desired temperature. Storing living seeds at room temperature (e.g. about 15° C. to about 25° C. in moderate climates, or about 25° C. to about 40° C. in warmer climates) is by far the cheapest and easiest option, but this may often be detrimental for the seed quality.
In the research leading to this invention it was found that especially at higher temperatures the positive effect of oxygen absorbers on the storability of living seeds is very pronounced. This makes the use of oxygen absorbers inside seed packaging very attractive, because it allows the storage of packages containing living plant seeds at ambient room temperature for a prolonged period of time without a significant loss of seed viability, even in warm environments. For commercial storage locations of plant seeds (such as shops or warehouses) this invention thus largely obviates the investment in cooling equipment for the purpose of storing seeds, such as refrigerators or freezers.
Especially in warm climates this is an enormous benefit, as seed packages to which at least one oxygen absorber has been added may be stored at room temperature, even if the ambient temperature is e.g. about 30° C. Without the inclusion of oxygen absorbers inside the storage container the quality of the stored seeds would rapidly decrease over time, especially if the seeds had been primed and/or pilled and/or coated, as is shown in the Examples. The use of oxygen absorbers as outlined in this application ensures the prolonged storability and maintenance of viability of living seeds, even at higher ambient temperatures.
The use of oxygen absorbers in the method of the invention thus has two related effects. First, they maintain the viability of living seeds during storage allowing the seeds to be kept at higher temperatures. In addition, the overall storability of pre-treated seeds, in particular of pilled and primed seeds, is prolonged.
Different types of oxygen absorbers that are commercially available on the market are e.g. the following: RP (manufactured by Mitsubishi Gas Chemical Company), AGELESS (manufactured by Mitsubishi Gas Chemical Company), PharmaKeep (manufactured by Mitsubishi Gas Chemical Company), StabilOx (manufactured by Multisorb Technologies), WELL PACK (manufactured by TAISEI Co.), Ever Fresh (manufactured by Torishige Sangyo Co.), Oxy-Eater (manufactured by Ueno Fine Chemicals Industry), KEEPIT (manufactured by Dorency Co.), KEPLON (manufactured by Keplon Co.), SANSO-CUT (manufactured by Iris fineproducts Co.), SANSORESU (manufactured by Hakuyo), Sequl (manufactured by Nisso Jushi Co.), TAMOTSU (manufactured by OhE Chemicals), VITALON (manufactured by Tokiwa Sangyo), Modulan (manufactured by Nippon Kayaku Food Techno Co.), Wonder Keep (manufactured by Powder Tech), and Keep Fresh Type C (manufactured by Toppan Printing Co.).
It was found according to the invention that the type of oxygen absorbers that binds oxygen without affecting the humidity of its environment is most suitable. This type is very useful for storing living seeds that are sensitive to changes in moisture content during storage.
Other types of oxygen absorbers also exist but these are not or less suitable for use in the invention.
One type needs to absorb moisture from the environment to be able to absorb oxygen. This type is only functional in relatively wet environments, and therefore unsuitable for storing living seeds.
A second type already contains moisture and can immediately absorb oxygen from the environment, without a need to absorb moisture from the environment. A feature of this second type is that it may release moisture into the environment, especially when this is a dry environment, which makes it unsuitable for living seed storage.
A third type binds both oxygen and moisture, so it requires no humidity for its function and it contains a desiccant to absorb moisture from its environment. The third type is suitable for use with living plant seeds that are drought-resistant. These three types thus alter the relative humidity of their environment.
Two examples produced by the Mitsubishi Gas Chemical Company are RP-A® and RP-K®. Both these oxygen absorbers are based on silica, and they may both be used in the method of the present invention, as is described in the Examples. However, an important difference between RP-A® and RP-K® lies in the ability of RP-K® to leave the air humidity unchanged (type 4, see above) while depleting it of oxygen, whereas RP-A® not only removes oxygen from the surrounding atmosphere, but also moisture (type 3, see above). According to the manufacturer RP-A® decreases the oxygen content inside a container to less than 0.1% within a day, while also reducing the relative humidity inside a container to less than 10% within an hour; according to the manufacturer RP-K® decreases the oxygen content inside a container to less than 0.1% within two days, while not affecting moisture content. For plant seeds that are tolerant to desiccation both types of oxygen absorbers are equally good, as shown in the Examples, but it was observed that for plant seeds that are sensitive to extreme drying the use of RP-K® is preferred. Both types work well at a broad temperature range (e.g. at −20° C. and at 30° C.), and especially at temperatures above 0° C. the effect on seed storability is very significant and pronounced.
The composition of RP-A® is as follows: mordenite, 10 to 50% Na8[(AlO2)8(SiO2)40]×24 H2O, 10 to 45% calcium oxide, 5 to 10% unsaturated organic compounds, 10 to 30% polyethylene, 5 to 15% activated carbon. According to the manufacturer, RP-A® is mainly intended for use with metal artifacts.
The composition of RP-K® is as follows: 10 to 40% diatomaceous earth, 1 to 20% calcium hydroxide, 10 to 25% unsaturated organic compounds, 15 to 35% polyethylene, 10 to 35% inorganic absorbent. According to the manufacturer, RP-K® is mainly intended for use with organic artifacts that require a special amount of moisture. However, its use with living material that is intended to be kept alive has never been proposed, suggested or tested.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.